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-12- <br />possibility of flash flooding in the design construction, and operation of <br />major engineering works, simply on the strength of recent experience is to <br />court disaster. In this report, the flood potential that exists in the <br />vicinity of the Rienau t4ine area is evaluated. A drainage plan for coping <br />with this extreme runoff ran suhseouPntly 6e developed based on these data. <br />2. PMTS Flood Potential in the Vicinity of Rienau Mine <br />The tributaries of Lurtis Creek in the vicinity of Rienau Mine (Figure 4) <br />.... <br />drain from less than 15 to more than 200 acres; hence runoff resulting from a <br />short intense burst of rainfall will produce the highest peaks. The PMTS <br />suggested for design 6y the USBR (1973) is a point rainfall of approximately <br />7.0 inches in one hour as shovm in Figure 5. Storm runoff was determined for <br />three small watersheds (Figure 4), and a potential flood hydrograph was derived <br />using guidelines recommended by the USBR (Appendix III - A). <br />These hydrographs for the PMiS are shown in Figure 6 They are <br />based on an antecedent moisture condition (AMC) II, curve number (CN) 75, and <br />a 7.0-inch point rainfall. Of the 7-inch rainfall, 4.2 inches would result <br />as surface runoff. It would produce the peak f]ows and volumes from each <br />watershed as summarized in Table 3. <br />Table 3 - PMTS Flood Potential in the Vicinity of Rienau Mine <br />4latershed Number Area Peak Discharge Volume <br />(Figure 2) (acres} (c.f.s.) (acre-feet) <br />1 271 ~ 2,300 95 <br />2 245 1,975 86 <br />3 13.3 132 4.7 <br />`- Relationship; between watershed area, peak discharge and volume are <br />found in Figure 7 <br />